Dynamic modeling and feature analysis of wind turbine with variable ratio gearbox

The paper investigates a new type of wind turbine embedded with variable ratio gearbox (VRG) that is capable of dynamically adjusting its transmission ratio between the turbine rotor and the generator. Such wind turbine, when controlled properly, is able to maintain the generator to operated at constant speed, which allows for the conventional synchronous generator to be used to build a wind turbine with grid-friendly features. The fundamental structure and the operational mechanism for the VRG based wind turbine (VRGWT) are examined and analyzed. To further reveal the salient features of the wind turbine, a three-mass dynamic model is proposed with consideration of torsional flexibility of the drive train shaft between the rotor and the generator. Theoretical analysis and numerical simulation show that maximum power point tracking (MPPT) can be achieved when the generator speed is kept constant, confirming the high conversion efficiency and grid-friendly features of the VRGWT.